Magnetic reconnection is a fundamental process that rapidly converts energy from the magnetic field to plasma. Recent studies have shown that a large parallel electric field (E) can appear in guide-field reconnection, and its magnitude can be several times larger than the reconnection electric field. However, the generation of this large E is still not fully understood, and the reaction of electrons to this E has not been fully investigated. In this study, we focus on these issues in a strong guide-field reconnection event (the normalized guide field is ~ 1.5) from Magnetospheric Multiscale (MMS) observations. With the presence of a large E in the electron current sheet, electrons are accelerated when streaming into this E region from one direction, and decelerated from the other direction. Some decelerated electrons can reduce the parallel speed to ~ 0 to form relatively isotropic electron distributions at one side of the electron current sheet, as the estimated acceleration potential (Φ ~ 2 kV) satisfies the relation eΦ ≥ kT, where T is the electron temperature parallel to the magnetic field. Therefore, a large E is generated to balance the parallel electron pressure gradient across the electron current sheet, since electrons at the other side of the current sheet are still anisotropic. Based on these observations, we further show that the electron beta is an important parameter in guide-field reconnection, providing a new perspective to solve the large parallel electric field puzzle in guide-field reconnection.

How to cite: Tang, B., Wang, H., Li, W., Zhang, Y., Graham, D., Khotyaintsev, Y., Gao, C., Guo, X., and Wang, C.: Electron dynamics in guide-field magnetic reconnection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11279, https://doi.org/10.5194/egusphere-egu23-11279, 2023.

The Kelvin-Helmholtz instability (KHI) excited at the Earth’s magnetopause has been considered responsible for causing efficient mass and energy transfer across the magnetopause. Theoretical, numerical and observational studies have revealed that the evolution of the KHI and the resulting nonlinear vortex flow involve secondary processes. As a unique case of such multi-scale and inter-process couplings, we recently reported observations of the MHD-scale KH waves and embedded smaller-scale phenomena in data from NASA’s Magnetospheric Multiscale (MMS) mission at the dusk- flank magnetopause during southward interplanetary magnetic field (IMF) conditions. Given quantitative consistencies with corresponding fully-kinetic particle-in-cell (PIC) simulations designed for this event, the MMS observations demonstrate the onset of the Lower-Hybrid Drift Instability (LHDI) during the nonlinear phase of the KHI and the subsequent turbulence and mixing of plasmas near the boundary layer.

In this study, we further explored this southward IMF KHI event and found signatures of magnetic reconnection in an electron-scale current sheet observed in the KH vortex-driven LHDI turbulence. This reconnection event was observed under high guide field conditions and features a super-Alfvénic electron outflow, a Hall perturbation of the magnetic field and enhanced energy conversion. Results from a high-resolution PIC simulation designed for this reconnecting current sheet suggest a highly dynamical current sheet evolution, quantitatively consistent with the observations made by MMS.

In addition, results from statistical studies utilizing data from several KH wave/vortex edge crossings throughout this southward IMF KH event show that the formation of electron-scale current sheets due to the interplay of the KHI and LHDI would be a ubiquitous phenomenon at least under the observed conditions of this magnetopause event and thus an important factor in the study of cross-scale energy transfer of the KHI.

How to cite: Blasl, K. A., Nakamura, T., Nakamura, R., Settino, A., Vörös, Z., Hosner, M., Schmid, D., Volwerk, M., Roberts, O. W., Panov, E., Liu, Y.-H., Plaschke, F., Hasegawa, H., Stawarz, J., and Holmes, J. C.: Electron-scale reconnecting current sheet formed within the lower hybrid wave-active region of Kelvin-Helmholtz waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6702, https://doi.org/10.5194/egusphere-egu23-6702, 2023.

Magnetic reconnection interlinks different regions of plasmas by converting magnetic energy into plasma heating and energization of particles. It causes abrupt changes in the temperature, density, field strength and flow speed. The physical mechanism behind charge particle energization during magnetic reconnection is best explained by the concept of double layers (DLs) and associated parallel electric fields. In-situ observations of reconnection sites by Magnetospheric Multi Scale (MMS), THEMIS and FAST have confirmed that charge particle energization in these regions is associated with large parallel electric fields in auroral regions, Earth’s plasma sheet and separatrix region of Earth’s magnetosphere. The reported literature motivated us to investigate double layers and associated electric field at the reported sites by using multi-fluid theory for electron-ion plasma and employing fully nonlinear Sagdeev potential approach. We have considered the ion inertial effect whereas electrons are assumed to be non-Maxwellian following (r, q) distribution function. In particular, parallel electric fields associated with Alfvenic double layer have been investigated at non-Maxwellian effective temperature scales and then compared with the observations. We have seen that the characteristics of DLs associated with the kinetic Alfvén waves are significantly modified due to the nonthermal parameters r and q, propagation angle 𝜃, and Alfvénic Mach number 𝑀_A. Our current study supports both the compressive and rarefactive double layer structures.

How to cite: Khalid, S. and Qureshi, M. N. S.: Parallel Electric Field and Double Layers at Non-Maxwellian Effective Temperature Scales in Near Earth Space Plasmas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5905, https://doi.org/10.5194/egusphere-egu23-5905, 2023.

High-speed electron flows play an important role in the energy dissipation and conversion in the terrestrial magnetosphere and are widely observed in regions related to magnetic reconnection, e.g., the vicinity of electron diffusion regions (EDRs), and separatrix layers. NASA’s Magnetospheric Multiscale mission was designed to resolve the electron-scale kinetic processes of Earth’s magnetosphere. Here, we perform a systematic survey of high-speed electron flows in the terrestrial magnetotail using the MMS observations from 2017 to 2021. The high-speed electron flows are characterized by electron bulk speeds larger than 5000 km/s. We identified 649 events. Those events demonstrate unambiguous dawn-dusk asymmetry, and 73% of them locate in the dusk magnetotail. The selected events are found in EDRs, the reconnection separatrix boundary layer, and the lobe region. More than 70% of the events are identified in the separatrix boundary layer and the lobe region and are aligned with the ambient magnetic field. 75 cases, with magnetic field magnitude smaller than 5 nT, locate near the plasma-sheet neutral line. Approximately 20 cases among them have EDR signatures, and those high-speed electron flows are directed arbitrarily with respect to the ambient magnetic field. We also show other statistical properties of the events, including electron bulk speed, electron number density, and temperature anisotropy. 

How to cite: Liu, H., Li, W., Tang, B., Norgren, C., Graham, D., Khotyaintsev, Y., Gershman, D., Burch, J., and Wang, C.: Statistics of the high-speed electron flows in the magnetotail, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10735, https://doi.org/10.5194/egusphere-egu23-10735, 2023.

A long-outstanding issue in fundamental plasma physics is how magnetic energy is finally dissipated in kinetic scale in the turbulent plasma. Based on the Magnetospheric Multiscale mission data in the plasma turbulence driven by magnetotail reconnection, we establish the quantitative relation between energy conversion (J·E , J is current density and E is electric field) and current density (J). The results show that the magnetic energy is primarily released in the perpendicular directions (up to 90%), in the region with current density less than 2.3 J_rms, where J_rms  is the root mean square value of the total current density J. In the relatively weak current region (< 1.0 J_rms ), the ions get most of the released energy while the largely negative energy conversion rate of the electrons means a dynamo action. In the strong currents (>1.0 J_rms), the ion energization was negligible and the electrons are significantly energized. Moreover, a linearly increasing relationship was established between J·E and J. The observations indicate that ions overall dominate energy conversion in turbulence, but the electron dynamics are crucial for energy conversion in intense currents and the turbulence evolution.

How to cite: Li, X., Wang, R., Huang, C., Lu, Q., and Lu, S.: Energy Conversion and Partition in Plasma Turbulence Driven by Magnetotail Reconnection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3017, https://doi.org/10.5194/egusphere-egu23-3017, 2023.

The terrestrial magnetosheath (MS) represents a turbulent, high-beta, compressional, sporadically Alfvenic environment which contains the shocked solar wind (SW) magnetized plasma permeated with waves, instabilities and structures of various origins. In the processes of interaction of the structured SW with the shock and the MS, the electromagnetic, kinetic and thermal energies are transported between locations,  transferred between scales, conversed between each other and finally dissipated. Similarly to the SW case the energy transfer in MS is expected to be manifested in typical scalings seen in power spectral densities of various field and plasma parameters  over the fluid (inertial-range) and kinetic ion-electron scales. However, near the sub-solar dayside MS the inertial-range turbulent cascade is usually absent, while the kinetic range scaling roughly remains the same as in the SW. Observations of short magnetic correlation lengths near the sub-solar MS also confirm the absence of large-scale magnetic fluctuations which could populate the inertial-range of scales. Without the inertial range energy cascade the kinetic range turbulence should exhibit a fast decay downstream of the shock, but it is not observed. We argue that to understand the spectral scalings in the MS the whole energy budget has to be considered including possible nonlocal energy transfer terms. By using MMS data in the MS we show that, when the inertial range is present, the turbulent energy dissipation rate can be estimated by the energy transfer rate from both the Yaglom law and from the pressure-strain interaction term. When the inertial range is absent and the Yaglom law cannot be used,  the dissipation rate can still be estimated by using the pressure-strain term.

How to cite: Vörös, Z., Roberts, O. W., Sorriso-Valvo, L., Yordanova, E., Narita, Y., Nakamura, R., and Plaschke, F.: Turbulent energy transfer and dissipation in the terrestrial magnetosheath, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6253, https://doi.org/10.5194/egusphere-egu23-6253, 2023.

The Kelvin-Helmholtz (KH) instability is a shear-driven instability commonly observed at the Earth’s magnetopause under different solar wind conditions. The evolution of the KH instability is characterised by the nonlinear coupling of different modes, which tend to generate smaller and smaller vortices along the shear layer. Such a process leads to the conversion of energy due to the large-scale motion of the shear flow into heat contributing to the local heating and the generation of a turbulent environment. On the other hand, it allows the entry of the dense and cold solar wind plasma into the tenuous and hot magnetosphere, thus favoring the mixing of these two different regions.

In this context, we introduce a new quantity, the so-called mixing parameter, which can identify the vortex boundaries and distinguish among different types of KH structures crossed by the spacecraft. The mixing parameter exploits the well distinct particle energies which characterise the magnetosphere and magnetosheath plasmas by using only single-spacecraft measurements [1]. The mixing parameter is therefore used to conduct a statistical analysis of the evolution of KH structures observed by the Magnetospheric Multiscale mission in the near Earth’s environment for two specific interplanetary magnetic field configurations: northward and southward. Moreover, in situ measurements are compared with kinetic KH instability simulations modeling realistic conditions observed by the satellites. The good agreement between synthetic data and in situ observations further strengthen our interpretation of the mixing parameter features and results.

[1] Settino, A., et al. (2022) Journal of Geophysical Research: Space Physics, 127, e2021JA029758.

How to cite: Settino, A., Nakamura, R., Blasl, K. A., Nakamura, T., Perrone, D., Valentini, F., Roberts, O. W., Panov, E., Vörös, Z., Volwerk, M., Schmid, D., Hosner, M., Graham, D. B., and Khotyaintsev, Y. V.: Plasma mixing during active Kelvin-Helmholtz instability at the Earth’s magnetopause under different interplanetary magnetic field configurations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12262, https://doi.org/10.5194/egusphere-egu23-12262, 2023.

We model plasma turbulence in the near-Sun solar wind by means of a high-resolution fully kinetic simulation initialised with average plasma conditions measured by Parker Solar Probe during its first solar encounter. Once turbulence is fully developed, the power spectra of the plasma and electromagnetic fluctuations exhibit clear power-law intervals down to sub-electron scales. Our simulation models the electron-scale electric field fluctuations with unprecedented accuracy. This allows us to perform the first detailed analysis of the different terms of the electric field in the generalised Ohm's law (MHD, Hall, and electron pressure terms) at ion and electron scales, both in physical space and in Fourier space. Such analysis suggests rewriting the Ohm’s law in a different form, which disentangles the contribution of different underlying plasma mechanisms, characterising the nature of the electric field fluctuations in the different range of scales. This provides a new insight on how energy in the turbulent electromagnetic fields is transferred through ion and electron scales and seems to favour the role of pressure-balanced structures versus waves. We finally test our assumptions and numerical results by means of a statistical analysis using magnetic field, electric field, and electron density data from Solar Orbiter and Parker Solar Probe. Preliminary results show good agreement with our theoretical expectations inspired by our simulation.

How to cite: Franci, L., Papini, E., Del Sarto, D., Micera, A., Stawarz, J., Horbury, T., Lapenta, G., Lewis, H., Salem, C., Landi, S., Hellinger, P., Matteini, L., Cicone, A., Piersanti, M., Innocenti, M. E., Maksimovic, M., and Burgess, D.: On the nature of electric field fluctuations in the near-Sun solar wind and its implication for the turbulent energy transfer at ion and electron scales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15616, https://doi.org/10.5194/egusphere-egu23-15616, 2023.

Heliospheric shocks associated with interplanetary coronal mass ejections (ICMEs) were observed by Wind, and DSCOVR at L1, STEREO spacecraft at ~1AU, and recently by the Parker Solar Probe in the inner heliosphere. The magnetic structure and the downstream magnetic oscillations were detected by Wind with 10.9 samples/s and DSCOVR with 50 samples/s. However, the velocity distributions of the protons are available at much lower cadence, and the potentially important interaction between  the alpha particles and  the heliospheric shocks are difficult to obtain directly from present data. Since the alpha particles in the solar wind are the second most abundant ion that can carry significant energy, momentum and mass flux of the solar wind, the alphas can significantly affect the propagation of these shocks. Recently, using hybrid-(PIC) models we studied the effects of alpha particles on the structure and magnetic oscillations of oblique high Mach number heliospheric shocks, and found that the magnetic and density structures of these shocks are significantly affected by the alpha particles with typical solar wind relative abundances. Here, we extend the study and report the results of new hybrid models of oblique shocks guided by observations. We investigate the typical observed relative solar wind abundances of alphas, Mach numbers, and shock normal directions, and compare the results for the various shock parameters. We model the effects of alpha particles properties on the shock ramp, wake, and downstream oscillations and study the properties of proton and alpha particle velocity distribution functions (VDFs) and the kinetic waves downstream of the shocks in the inner heliosphere. We expand the model and study for the first time the effects of relative streaming of proton-alpha ion populations as well as the ion anisotropies on the shock propagation. We investigate the effects of the ion kinetic properties on the heliospheric shock structures and discuss how the modeling results can improve the interpretation of spacecraft observations of these shocks. 

How to cite: Ofman, L., Wilson, L. B., Nieves-Chinchilla, T., Jian, L., and Szabo, A.: Investigating the interactions of alpha particles in collisionless oblique heliospheric shocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16725, https://doi.org/10.5194/egusphere-egu23-16725, 2023.

Turbulent states of motion are almost unavoidable in fluids, gases, and plasmas. The ubiquitous presence of turbulence largely contributes to the central role that its study holds in many research fields. This work focuses on space and astrophysical plasmas, where magnetohydrodynamic turbulence is observed nearly everywhere. However, it builds on an issue that is shared by all turbulence-related field of studies: direct numerical simulations (DNS), required to verify turbulent states properties such as scaling law behaviors, require substantial computing resources.

The presentation will introduce the audience to BxC^[1], an analytic generator of realistic-looking turbulent magnetic fields, that computes 3D O(1000³ grid points) solenoidal vector fields in minutes to hours on desktops. The model is inspired by recent developments in 3D incompressible fluid turbulence theory: intermittent, multifractal random fields are generated through non-linear transformations of a Gaussian white noise vector, combined to specifically designed geometrical constructions. Furthermore, the model is implemented starting from a modified Biot-Savart law, which allows for a clear interpretation of the BxC parameters.

The turbulent magnetic field realized with BxC is then compared and validated against a much more computationally expensive DNS in terms of: (i) characteristic sheet-like structures of current density, (ii) volume-filling aspects across current intensity, (iii) power-spectral behaviour, (iv) probability distribution functions of increments for magnetic field and current density, structure functions, spectra of exponents, and (v) partial variance of increments.

[1] Durrive, J.-B., Changmai, M., Keppens, R., Lesaffre, P., Maci, D., and Momferatos, G. (2022). Swift generator for three-dimensional magnetohydrodynamic turbulence. Phys. Rev. E, 106:025307

How to cite: Maci, D., Keppens, R., and Bacchini, F.: Swift generator for 3D magnetohydrodynamic turbulence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3604, https://doi.org/10.5194/egusphere-egu23-3604, 2023.